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Letters to the Editor
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Adverse drug reactions
Miconazole oral gel and warfarin
From Miss S. Baker, MRPharmS
I have become increasingly concerned about the lack of awareness among
community pharmacists about the potentiation effect that miconazole oral
gel has on warfarin.
I run community based INR clinics in County Durham, and over the past year
I have had two cases where miconazole oral gel has been sold to patients taking
warfarin. In both cases, the patient’s INR increased drastically from
their stable 2–3 range, to 15 in the first case and 9.5 in the second
case.
The first patient had to be admitted to hospital for vitamin K treatment and
the second patient was admitted with haematurea. The risk of bleeding to the
patient at this high INR cannot be under-estimated. Yellow cards have been
completed on the above reactions. A third patient was sold the gel, but checked
with the warfarin clinic first and we stopped her using it.
A quick literature search of the interaction shows numerous examples of dangerously
high INRs when miconazole oral gel is used with warfarin. This interaction
has a black dot in the BNF, yet patients are being placed at high risk of bleeding
by being given the oral gel.
Miconazole oral gel should never be used concomitantly with warfarin, whether
prescribed by a GP or sold OTC. It may be that extra training is needed for
pharmacy staff on warfarin interactions, or that the packaging of miconazole
gel should be altered to include a warning on use with warfarin. If the gel
cannot be sold safely, then that seems to beg the question, should it revert
back
to a POM?
Sonia Baker
Warfarin Pharmacist
Intrahealth Ltd, Co Durham
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The
Pharmaceutical Journal